build(deps): bump actix-web in /atcoder-problems-backend

Bumps [actix-web](https://github.com/actix/actix-web) from 4.1.0 to 4.2.1.
- [Release notes](https://github.com/actix/actix-web/releases)
- [Changelog](https://github.com/actix/actix-web/blob/master/CHANGES.md)
- [Commits](actix/actix-web@web-v4.1.0...web-v4.2.1)

---
updated-dependencies:
- dependency-name: actix-web
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

atcoder-problems-backend/Cargo.lock

@@ -23,7 +23,7 @@ sql-client = { path = "./sql-client" }
 atcoder-client = { path = "./atcoder-client" }
 
 # Web framework
-actix-web = "4.1.0"
+actix-web = "4.2.1"
 actix-service = "2.0.2"
 reqwest = { version = "0.11", features = ["json"] }